30.8.4 Viewing One Outline in Multiple Views

You can display two views of a single outline at the same time, in
different windows. To do this, you must create an indirect buffer using
M-x make-indirect-buffer. The first argument of this command is
the existing outline buffer name, and its second argument is the name to
use for the new indirect buffer. See section Indirect Buffers.

Once the indirect buffer exists, you can display it in a window in the
normal fashion, with C-x 4 b or other Emacs commands. The Outline
mode commands to show and hide parts of the text operate on each buffer
independently; as a result, each buffer can have its own view. If you
want more than two views on the same outline, create additional indirect
buffers.